Overrunning roller clutches provide for selective relative rotation between a pair of coaxial clutch races through the use of spring energized rollers that jam between the races in one direction, but free wheel in the other. Each of the races is generally annular or ring shaped, and each has a pair of flat end faces that determine its axial thickness. Each race may shift axially back and forth to an extent as the clutch operates, however, especiallY if the clutch is used in a vehicle transmission environment where there are large, rapidly shifting axial forces caused by actuating pistons and the like. In such an environment, the race end faces may be abutted with, or very close to, other structures, and may see significant axial thrust loads therefrom.
Besides the flat end faces, the clutch races have inner surfaces that confront one another across an annular space. One race, the pathway race, has an inner surface that is simply a smooth cylindrical pathway. The other race, the cam race has an inner surface that is more complex. The cam race surface is made up of a plurality of cam ramps that slope in one direction down to a cam hook, which slopes up much more sharply in the other direction. Each cam ramp-cam hook pair, which forms an asymmetrical V when viewed along the clutch axis, is separated by a partially cylindrical bearing surface. The races serve to keep the rollers in their proper radial and circumferential location, because the rollers are in continual contact with the cam ramps and pathway, both during lockup and overrun. During lockup, the rollers are jammed between the cam ramps and pathway, and cannot move significantly in any direction. During overrun, the energizing springs push the rollers into contact against the cam ramps and pathway, ready to lockup again. The axial position of the rollers, however, must be maintained by another clutch component, known as the cage.
The cage, which is installed to the cam race radially between the races, provides two basic functions, which determine its shape. First, it retains the rollers and springs, both before installation and during clutch operation, for which it has a series of generally rectangular pockets that sit over the cam ramps. Second, it maintains the races coaxial to one another during clutch operation, for which it has a plurality of close fitting journal blocks that sit over the bearing surfaces. Techniques exist for molding the pockets and journal blocks together as a unitary cage with only two, axially parting dies. This method is generally known as bypass molding, and is very cost effective. It is highly desirable, therefore, that the shape of any structure molded with the cage be amenable to bypass molding.
Another consideration that has driven the shape of the cage is the necessity keeping the cage properly positioned and aligned between the races during clutch operation. The radial position of the cage, like the rollers, is basically fixed, since its journal blocks are closely confined between the races. However, during overrun, the pathway rides over the journal blocks are closely confined between the races. However, during overrun, the pathway rides over the journal blocks, creating friction that could tend to rotate the cage out of its proper circumferential position relative to the cam race. To prevent that, the cage is molded with a series of reaction faces that abut the cam hooks and stop the cage from being rotated out of position. During lockup, the energizing springs push off of the jammed rollers and against the cage pockets to push the reaction faces against the cam hooks. To maintain the axial position of the cage, and by implication of the rollers, the cage is typically molded with reaction ears at the edge of the cage that are intended to abut the end faces of one of the races, usually the cam race. The cage is thereby prevented from shifting axially significantly. The reaction ears can be made bypass moldable if they are alternated around the two axial sides of the cage, so as to have no mutual circumferential overlap.
Cage shape and size is also determined by the need for easy cage installation. The reaction ears are deliberately made short, in the radial sense, at least on the lead axial side of the cage, that is, the side of the cage that is pushed axially over the cam race first when the cage is installed. By doing so, the cage can initially be turned in one direction to a position relative to the cam race where the reaction ears on the lead side of the cage are aligned with the notch of the V's. This gives enough clearance for the reaction ears to pass through the notch as the cage is pushed over the cam race. Then, the cage is rotated in the other direction until the reaction faces abut the cam hooks and the reaction ears simultaneously move over the end faces of the cam race. This cage installation method has been termed "twist lock." Finally, the pathway race is pushed over the rollers and rotated in the same direction that the cage was twisted.
There are limits to how much resistance to axial cage shifting reaction ears of such a design can provide. As noted, the reaction ears on the lead side of the cage must be fairly short to allow them to pass through. Also, they must alternate around the two sides of the cage if they are to be bypass moldable, which limits their number on each side to half the total number of cam ramps. While the reaction ears on the trailing side of the cage can be made larger, those on both sides of the cage necessarily overlay the end faces of the cam race. Any adjacent components that are thrust toward the cam race end faces may, therefore, collide with the reaction ears.